Automobile transmissions have recently tended to use low viscosity oil so as to attain AT, CVT, low fuel consumption, etc., for the transmission. In an environment where low viscosity oil is used, the surface-start abrasion, which results in a very short bearing life, sometimes occurs in the inner ring raceway surface, where the surface pressure is high, due to poor lubrication when such adverse conditions as (1) high oil temperature, (2) little oil quantity, and (3) pre-load escape, simultaneously happen.
As for measures against this short bearing life due to the surface-start abrasion, a direct and effective solution is to reduce the maximum surface pressure. To reduce the maximum surface pressure, it is necessary to change the bearing size or to increase the number of rollers of the bearing if the bearing size is not to be changed. To increase the number of rollers without decreasing the roller diameter, it is necessary to narrow the distance between pockets in the cage. To this end, however, the pitch circle of the cage has to be increased to draw the cage as close as possible to the outer ring.
As an example in which the cage is drawn to the side until it touches the inner diameter surface of the outer ring, there is a tapered roller bearing shown in FIG. 1 (refer to Japanese Patent Laid-Open No. 2003-28165). In this tapered roller bearing 11, the outer peripheral surfaces of the small and large diameter annular sections 12a and 12b of the cage 12 are placed in slide contact with the inner diameter surface of the outer ring 13 so as to guide the cage 12, and the outer diameter surface of each pillar 12c of the cage 12 is formed with a recess 14 for suppressing drag torque, thereby maintaining the non-contact state between the outer diameter surfaces of the pillars 12c and the raceway surface 13a of the outer ring 13. The cage 12 has a small diameter annular section 12a, a large diameter annular section 12b, and a plurality of pillars 12c which axially connect the small and large diameter annular sections 12a and 12b and which are formed with recesses 14 in the outer peripheral surface thereof. And disposed between successive pillars 12c are a plurality of pockets for rollably receiving tapered rollers 15. The small diameter annular section 12a is provided with a flange 12d integrally extending to the inner diameter side. The tapered roller bearing of FIG. 1 is an example intended to improve the strength of the cage 12, wherein the cage 12 is drawn to the side until it touches the inner diameter surface of the outer ring 13 in order to increase the peripheral width of the pillars 12c of the cage 12.